Effect of head position on cephalometric evaluation of the soft-tissue facial profile

Objectives: During a cone beam CT scan, the patient is in an upright or supine position. This position depends on the brand and type of the scanner. The aims of this study are: (1) to investigate if the head position has an effect on cephalometric evaluation of the soft-tissue facial profile, comparing the recordings in natural head position (NHP) and supine head position (SHP) and (2) to investigate if age, gender and body mass index (BMI) are contributing factors to the effect of the head position. Methods: 90 subjects were photographed in profile both in NHP and in SHP. 12 soft-tissue angular and linear cephalometric values were calculated. Two-way random intraclass correlation coefficients were calculated to determine observer reliability. Paired t-tests and linear regression analyses were performed to investigate the differences between the head positions and the influence of age, gender and BMI. Results: Intraobserver reliability was generally high. Paired t-tests showed significant changes as a result of head positioning (p < 0.0001) in 9 of the 12 measurements. These differences were small and clinically not relevant, except for the "lower face-throat angle". Regression analysis revealed no relevant influence of age, gender and BMI. Conclusions: Cephalometric soft-tissue evaluation from a recording in SHP is generally reliable, except for the throat-chin area where a clinically relevant difference was found. The contour of the submandibular tissues in SHP causes the chin to appear more prominently. This can cause incorrect orthodontic diagnosis and treatment planning.